Auto-tuned ramp generator

ABSTRACT

An auto-tuned ramp generator and a method for generating a sawtooth signal are provided. In the method and apparatus, a sawtooth signal is compared to a first reference voltage and a second reference voltage. In response to determining that the sawtooth signal does not exceed the first reference voltage, the voltage level of the sawtooth signal is increased. In response to determining that the sawtooth signal exceeds the second reference voltage, the voltage level of the sawtooth signal is decreased. The voltage level the sawtooth signal is retained if the sawtooth signal remains between the first and second reference voltages.

BACKGROUND Technical Field

This application is directed to a ramp or sawtooth signal generator and,in particular, a ramp or sawtooth signal generator that generates asawtooth signal exhibiting consistent properties, such as peak voltage.

Description of the Related Art

Ramp generators are ubiquitous in power regulation and control circuitsincluding controllers for converters, such as buck, boost or buck-boostDC-DC converters. Many converter controllers are “output levelresponsive,” and, accordingly, maintain a converter output at a desiredlevel by responding to deviations in the output level and producing achange in the output that is opposite to the deviation. A convertercontroller may utilize a sawtooth signal in controlling the converter.

The accuracy of the sawtooth signal affects the operation of thecontroller. For example, deviations in the peaks of the sawtooth signalresult in inconsistent regulation. The sawtooth signal is susceptible toprocess spreads, frequency changes, power supply variations, temperaturevariations and post-production factors, such as aging and soldering. Itis, accordingly, desirable to have an auto-tuned ramp or sawtoothgenerator that can generate a sawtooth signal that isvariation-resistant and has consistent properties, such as peak voltage.

BRIEF SUMMARY

In an embodiment, a sawtooth signal generator includes a sawtooth signalgeneration stage configured to: receive a control signal; and generate asawtooth signal based on the control signal. In an embodiment, thesawtooth signal generator includes a first comparator configured to:receive a first reference voltage; receive the sawtooth signal; comparethe sawtooth signal with the first reference voltage; and output a firstcomparison signal that is asserted when the sawtooth signal exceeds thefirst reference voltage and deasserted when the sawtooth signal does notexceed the first reference voltage. In an embodiment, the sawtoothsignal generator includes a second comparator configured to: receive asecond reference voltage; receive the sawtooth signal; compare thesawtooth signal with the second reference voltage; and output a secondcomparison signal that is asserted when the sawtooth signal exceeds thesecond reference voltage and deasserted when the sawtooth signal doesnot exceed the second reference voltage. In an embodiment, the sawtoothsignal generator includes control logic configured to: receive the firstand second comparison signals; determine whether the first comparisonsignal is deasserted; in response to determining that the firstcomparison signal is deasserted, output the control signal commandingthe sawtooth signal generation stage to increase a voltage level of thesawtooth signal; determine whether the second comparison signal isasserted; and in response to determining that the second comparisonsignal is asserted, output the control signal commanding the sawtoothsignal generation stage to decrease the voltage level of the sawtoothsignal.

In an embodiment, the sawtooth signal generation stage includes: acurrent source having a control terminal configured to receive thecontrol signal, an anode coupled to a voltage supply node and a cathodecoupled to a sawtooth signal output node; a capacitance having a firstside coupled to the output of the sawtooth signal output node and asecond side coupled to a ground or reference node; and a switch having acontrol terminal configured to receive a reset signal, a firstconduction terminal coupled to the sawtooth signal output node, while asecond conduction terminal coupled to the ground or reference node.

In an embodiment, the current source is configured to: receive thecontrol signal; and adjust an output current provided at the cathodebased on the control signal. In an embodiment, the control logic isconfigured to: receive a clock signal; and output the reset signal basedon the clock signal, the reset signal when activated causes the switchto close and reset the sawtooth signal to a ground voltage of the groundnode or a reference voltage of a reference node.

In an embodiment, the control logic is configured to: determine that thefirst comparison signal is asserted and the second comparison signal isdeasserted; and in response to determining that the first comparisonsignal is asserted and the second comparison signal is deasserted,output the control signal commanding the sawtooth signal generationstage to retain the voltage level of the sawtooth signal. In anembodiment, the voltage level of the sawtooth signal is the peak voltageof the sawtooth signal.

In an embodiment, a controller for a converter includes a switchingstage configured to: receive a feedback voltage indicative of an outputvoltage of the converter, and a sawtooth signal; generate a controlsignal based on the feedback voltage and the sawtooth signal; and outputthe control signal for driving the converter. In an embodiment, thecontroller includes a sawtooth signal generator configured to: receive afirst reference voltage and a second reference voltage; determinewhether a voltage level of the sawtooth signal is below the firstreference voltage or greater than the second reference voltage; inresponse to determining that the voltage level of the sawtooth signal isbelow the first reference voltage, cause the voltage level of thesawtooth signal to increase; and in response to determining that thevoltage level of the sawtooth signal is greater than the secondreference voltage, cause the voltage level of the sawtooth signal todecrease.

In an embodiment, the sawtooth signal generator is configured to:determine whether the voltage level of the sawtooth signal is betweenthe first reference voltage and the second reference voltage; inresponse to determining that the voltage level of the sawtooth signal isbetween the first reference voltage and the second reference voltage,retain the voltage level of the sawtooth signal.

In an embodiment, the sawtooth signal generator is configured to:receive a clock signal for operating the converter; and cause thevoltage level of the sawtooth signal to be reset in response to theclock signal. In an embodiment, the sawtooth signal generator isconfigured to determine whether the voltage level of the sawtooth signalis below the first reference voltage or greater than the secondreference voltage prior to causing the voltage level of the sawtoothsignal to be reset.

In an embodiment, the sawtooth signal generator includes: a currentsource having a control terminal for receiving a control signal, ananode coupled to a voltage supply node, and a cathode coupled to asawtooth signal output node; a capacitance having a first side coupledto the sawtooth signal output node, and a second side coupled to aground or reference node; and a switch having a control terminal forreceiving a reset signal, a first conduction terminal coupled to thesawtooth signal output node, and a second conduction terminal coupled tothe ground or reference node. In an embodiment, the switch is configuredto transition to an electrically conductive state in response to theassertion of the reset signal to reset the sawtooth signal to areference voltage level.

In an embodiment, a method includes receiving a sawtooth signalgenerated by a sawtooth signal generation stage; comparing, by a firstcomparator, the sawtooth signal to a first reference voltage; comparing,by a second comparator, the sawtooth signal to a second referencevoltage; in response to determining, based on comparing the sawtoothsignal to the first reference voltage, that the sawtooth signal does notexceed the first reference voltage, causing a voltage level of thesawtooth signal to increase; and in response to determining, based oncomparing the sawtooth signal to the second reference voltage, that thesawtooth signal exceeds the second reference voltage, causing thevoltage level of the sawtooth signal to decrease.

In an embodiment, a method includes supplying, by a current source ofthe sawtooth signal generation stage, current to charge a capacitance;and drawing the sawtooth signal from a charge on a first side of thecapacitance. In an embodiment, causing the voltage level of the sawtoothsignal to increase includes outputting a signal to the current sourcecommanding the current source to increase a supply of current to thecapacitance.

In an embodiment, causing the voltage level of the sawtooth signal todecrease includes outputting a signal to the current source commandingthe current source to decrease a supply of current to the capacitance.In an embodiment, a method includes supplying the sawtooth signal to acontroller of a converter. In an embodiment, a method includes detectingthat a clock signal used to operate the converter transitioned betweenstates; and in response to detecting that the clock signal transitionedbetween states, resetting the sawtooth signal to a reference voltage. Inan embodiment, comparing the sawtooth signal to the first referencevoltage and comparing the sawtooth signal to the second referencevoltage is performed prior to resetting the sawtooth signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a system for controlling a converter.

FIG. 2 shows a circuit diagram of a ramp generator.

FIGS. 3A and 3B show timing diagrams of signals of the ramp generatordescribed with reference to FIG. 1.

FIG. 4 shows a flow diagram of a method for operating control logic ofthe ramp generator in accordance with an embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a system 100 for controlling a converter 102. The system100 includes the converter 102 and a controller 104. The controller 104includes a control stage 106 and a ramp generator 108 (also referred toherein as a sawtooth signal generator). The converter 102 may be anytype of system or device that receives an input voltage and a controlsignal and provides an output voltage based on the input voltage and thecontrol signal. For example, the converter 102 may be a DC-DC converter.The converter 102 may also be a buck converter, a boost converter or abuck-boost converter, among others. The controller 104 may be any typeof system or device that is configured to control the converter 102. Forexample, the controller 104 may generate the control signal and outputthe control signal to the converter 102. The converter 102 outputs adesired output voltage based on the control signal and the input voltageof the converter 102.

The ramp generator 108 may be any type of device configured to produce agradually changing signal. The changing signal may be a sawtooth with arepeating ramp and return to an initial value (such as a referencevoltage, ground voltage or zero voltage). The ramp generator 108 mayoperate using controlled capacitor charging, where a capacitor ischarged to a value.

The converter 102 is coupled to an input voltage node 110 and an outputvoltage node 112. The converter 102 receives the control signal. Theconverter 102 receives an input voltage (V_(IN)) at the input voltagenode 110. The converter 102 operates in accordance with the controlsignal and outputs an output voltage (V_(OUT)) at the output voltagenode 112. The control signal may dictate switching times of switches ofthe converter 102, which may cause the converter 102 to output theoutput voltage having a desired output voltage level. The converter 102may output the output voltage to a load 114 coupled between the outputvoltage node 112 and a ground node 116. The ground node 116 maygenerally be any reference voltage node.

The control stage 106 receives a signal representative of the outputvoltage. The control stage 106 also receives a sawtooth signal generatedby the ramp generator 108. The control stage 106 generates the controlsignal based at least in part on the signal representative of the outputvoltage and the sawtooth signal. The control stage 106 may also generatethe control signal based on a reference voltage representative of adesired output voltage level.

The accuracy of the operation of the system 100 and of the generatedoutput voltage is also dependent on the reliability of the sawtoothsignal. Variations in the sawtooth signal negatively affect theoperation of the system 100. For example, variation between peak heightsof the sawtooth signal over time makes the behavior of the converter 102unstable or unpredictable. Temperature conditions as well as noise andother factors may affect the sawtooth signal. Furthermore, power supplyvariation as well as frequency changes may cause the peaks of thesawtooth signal to vary over time. In some applications of DC-DCconverters, the frequency of the converter can be modified. Theembodiments described herein ensure that the peaks of the sawtoothsignal remain stable and fixed, which is of import in converters.Further, process spreads between different devices and postproductionaging or soldering may induce variations between sawtooth signalsgenerated by different devices.

FIG. 2 shows a circuit diagram of the ramp generator 108. The rampgenerator 108 includes a current source 120, a capacitance 122, a switch124, a first comparator 126, a second comparator 128 and control logic130. In the ramp generator 108, the current source 120, capacitance 122,and switch 124 form a sawtooth signal generation stage 131.

The current source 120 may be a controlled current source, whereby anoutput current of the current source is variable and is controlled usinga current source control signal provided to the current source 120. Thecurrent source 120 has an anode coupled to a voltage source node 132 anda cathode coupled to a sawtooth signal output node 133. The currentsource 120 also has a control terminal for receiving the current sourcecontrol signal. The capacitance 122 has a first side coupled to thesawtooth signal output node 133 and a second side coupled to a ground orreference node 134.

The switch 124, which may be a transistor, is coupled in parallel withthe capacitance 122 and, accordingly, has a first conduction terminalcoupled to the sawtooth signal output node 133 and a second conductionterminal coupled to the ground or reference node 134. The switch 124 hasa control terminal that receives a ramp termination control signal.

The first comparator 126 has a noninverting input coupled to thesawtooth signal output node 133 and an inverting input configured toreceive a first reference voltage (V_(REF1)). The first comparator 126has an output coupled to a first input of the control logic 130.

The second comparator 128 has a noninverting input coupled to thesawtooth signal output node 133 and an inverting input configured toreceive a second reference voltage (V_(REF2)). The second comparator 128has an output coupled to a second input of the control logic 130.

The control logic 130 also has a third input for receiving a clocksignal. In addition, the control logic 130 has a first output foroutputting the current source control signal and a second output foroutputting the ramp termination control signal.

In the ramp generator 108, the output sawtooth signal is provided at thesawtooth signal output node 133. As described herein, the ramp generator108 may be used to generate the sawtooth signal (or more generally aramp signal) having a peak that is between the first reference voltage(V_(REF1)) and the second reference voltage (V_(REF2)). The rampgenerator 108 controls the sawtooth signal to have a peak that isgreater than the first reference voltage (V_(REF1)) and smaller than thesecond reference voltage (V_(REF2)). Accordingly, a stable andvariation-resistant sawtooth signal is provided.

Initially, the current source 120 provides an output current thatcharges the capacitance 122. The capacitance 122 is charged over timeand as time elapses and more current is supplied by the current source120, the voltage differential across the capacitance 122 increases. Asthe voltage differential across the capacitance 122 increases so doesthe voltage level of the sawtooth signal taken at the sawtooth signaloutput node 133 (or the first side of the capacitance 122).

The sawtooth signal is also provided to the noninverting inputs of thefirst and second comparators 126, 128. The first comparator 126 comparesthe sawtooth signal to the first reference voltage (V_(REF1)). The firstcomparator 126 outputs a first comparison signal that is asserted whenthe sawtooth signal (or a voltage level thereof) meets or exceeds thefirst reference voltage (V_(REF1)). When the sawtooth signal does notexceed the first reference voltage (V_(REF1)), the first comparisonsignal may remain in the deasserted state. A signal may be asserted ifthe signal is activated or transitions to an active state, such as alogical one. Alternatively, a different convention may be adoptedwhereby deassertion, for example, the transitioning to a logical zero,of the first comparison signal is used to indicate that the sawtoothsignal has met or exceeded the first reference voltage (V_(REF1)).

Similarly, the second comparator 128 compares the sawtooth signal to thesecond reference voltage (V_(REF2)). The second comparator 128 outputs asecond comparison signal that is asserted when the sawtooth signal meetsor exceeds the second reference voltage (V_(REF2)) and that isdeasserted when the sawtooth signal does not exceed the second referencevoltage (V_(REF2)).

The control logic 130 receives the first comparison signal and thesecond comparison signal. Therefore, the control logic 130 receivesinformation indicating whether the sawtooth signal is below the firstreference voltage (V_(REF1)), between the first reference voltage(V_(REF1)) and the second reference voltage (V_(REF2)), or greater thanthe second reference voltage (V_(REF2)).

The control logic 130 also receives a clock signal. The control logic130 may be configured to cause the sawtooth signal to be reset or revertto a low voltage level (such as a voltage level of zero) at certaintimes according to the clock signal. For example, the sawtooth signalmay be reset at a rising edge of the clock signal, a falling edge of theclock signal, or at any other time during the clock signal or any othersignal related to the clock signal.

The control logic 130 may allow a voltage level of the sawtooth signalto increase over a duration of a clock cycle and reset the sawtoothsignal at a predefined point during the clock cycle, such as the risingor falling edge of the clock signal.

To reset the clock cycle sawtooth signal, the control logic 130 assertsthe ramp termination control signal. The ramp termination is provided toa control terminal of the switch 124. When the ramp termination controlsignal is asserted, the switch 124 transitions to the electricallyconductive state, and thereby couples the first side of the capacitance122 to the ground or reference node 134 and shorts the capacitance 122.As a result, the sawtooth signal is reset to the ground voltage of 0Volts (V) or the reference voltage.

The control logic 130 determines, based on the first and secondcomparison signals, whether a peak of the sawtooth signal (observedbefore shorting the capacitance 122) is between the first referencevoltage (V_(REF1)) and the second reference voltage (V_(REF2)), i.e.,within a desired range of voltage levels.

If the control logic 130 determines that the sawtooth signal did notexceed the first reference voltage (V_(REF1)), the control logic 130causes the current level output by the current source 120 to increase.The control logic 130 determines that the sawtooth signal did not exceedthe first reference voltage (V_(REF1)) when neither the first comparisonsignal nor the second comparison signal is asserted.

If the control logic 130 determines that the sawtooth signal exceededthe first reference voltage (V_(REF1)) and remained below the secondreference voltage (V_(REF2)), the control logic 130 retains the currentlevel output by the current source 120. The control logic 130 determinesthat the sawtooth signal remained between the two reference voltagelevels if the first comparison signal was asserted and the secondcomparison signal was not asserted.

If the control logic 130 determines that the sawtooth signal exceededthe second reference voltage (V_(REF2)), the control logic 130 causesthe current level output by the current source 120 to decrease. Thecontrol logic 130 determines that the sawtooth signal exceeded thesecond reference voltage (V_(REF2)) when both the first and secondcomparison signals get asserted.

The current source control signal may indicate a desired output currentlevel of the current source 120 and may command the current source 120to output the desired current level. For example, the current sourcecontrol signal may be a multi-bit or multilevel control signal, wherebyeach bit or level may be used to indicate a unique output current levelof the current source 120. The output current level of the currentsource 120 may be “stepped-up” or “stepped-down” using the currentsource control signal. For example, if the current source control signalis incremented, the output current level of the current source 120 maybe increased or “stepped-up,” and if the current source control signalis decremented, the output current level of the current source 120 maybe decreased or “stepped-down.” Retaining the current source controlsignal without changing its level causes the output current level of thecurrent source 120 to be retained without change.

Changing the current source 120 output current level causes the slope ofthe sawtooth signal (or ramp) to change. When the output current levelis increased, the voltage level of the sawtooth signal increases at afaster rate, thereby reaching a particular voltage level in a shorterperiod of time. Conversely, decreasing the output current level reducesthe rate at which the voltage level of the sawtooth signal climbs, andthe particular voltage level is reached after a longer period of time.Thus, if the sawtooth signal is reset at equal intervals, adjusting theoutput current level in effect adjusts the peak voltage levels of thesawtooth signal.

FIGS. 3A and 3B show timing diagrams 300 of signals of the rampgenerator 108 described with reference to FIG. 1. The timing diagram 300shows the sawtooth signal 302, the first comparison signal 304, thesecond comparison signal 306 and the current source control signal 308.In addition, the timing diagram 300 shows the first reference voltage310 and the second reference voltage 312.

In FIG. 3A, the sawtooth signal 302 initially increases over time and isreset at a first time instance 314. The control logic 130 determineswhether the first comparison signal 304 and the second comparison signal306 were asserted before the sawtooth signal 302 is reset to thereference voltage level. Because the first comparison signal 304 was notasserted, it may be concluded that the sawtooth signal 302 fell short ofthe first reference voltage 310. Accordingly, the control logic 130causes the output current of the current source 120 to increase. Thecontrol logic 130, in this example, increments a level of the currentsource control signal 308 from eight to nine.

Between the first time instance 314 and a second time instance 316, thecapacitance 122 is charged again. The sawtooth signal 302 reaches a peakcurrent level before the sawtooth signal 302 is reset at the second timeinstance 316. The control logic 130 determines that the first comparisonsignal 304 was asserted and the second comparison signal 306 was notasserted. Accordingly, the sawtooth signal 302 reached a peak betweenthe first and second reference voltages 310, 312. The control logic 130retains the current source control signal at its prior level. Similarly,when a third time instance 318 is reached, the sawtooth signal 302reaches a peak between the first and second reference voltages 310, 312.Accordingly, the control logic retains without change the current sourcecontrol signal.

In FIG. 3B, initially the current source control signal 308 has a levelof ten. A voltage level of the sawtooth signal 302 increases until thesawtooth signal 302 is reset at a fourth time instance 320. The peakvoltage level of the sawtooth signal 302 reached prior to the resettingexceeds the second reference voltage 312. As a result, the secondcomparison signal 306 (as well as the first comparison signal 304) isasserted. Assertion of the second comparison signal 306 is indicativethat the output current of the current source 120 is too elevated. Thecontrol logic 130 decrements the current source control signal 308 inorder to reduce the output current level of the current source 120.

Accordingly, between the fourth time instance 320 and a fifth timeinstance 322, the peak voltage level of the sawtooth signal 302 dropsbelow the second reference voltage 312 and remains above the firstreference voltage 310. In response, the control logic 130 does not alterthe state of the current source control signal 308. Similarly, thecontrol logic 130 retains a state of the current source control signal308 after a sixth time instance 324 in response to the sawtooth signal302 falling between the two reference voltages 310, 312.

FIG. 4 shows a flow diagram of a method 400 for operating the controllogic 130 in accordance with an embodiment. The method 400 may beimplemented using circuitry, such as a hardware circuit, or acontroller, such as a processor, microprocessor or microcontroller,among others. For example, the control logic 130 may be a circuit, suchas a digital circuit, or an external controller.

In the method 400, the control logic 130 receives, at 402, a firstcomparison signal that when asserted indicates that a sawtooth signalexceeds a first reference voltage. The control logic 130, at 404,receives a second comparison signal that when asserted indicates thatthe sawtooth signal exceeds a second reference voltage. The controllogic 130, at 406, determines whether the first comparison signal isdeasserted. If a positive determination is made at 406, at 408 thecontrol logic 130 outputs a control signal commanding a sawtooth signalgeneration stage to increase a voltage level of the sawtooth signal.Examples of the control signal include the control signal 308 describedwith reference to FIG. 3. For example, the control logic 130 mayincrease a level of the control signal, which may be a multi-bit signal.The control logic 130 may increase a level of the control signal to warnthat the voltage level of the sawtooth signal has to be increased. Asdescribed herein, a current source of the sawtooth signal generationstage may receive the control signal and correspondingly increase itsoutput current level. Increasing the output current level causes thevoltage level of the sawtooth signal to increase.

If a negative determination is made at 406, it may be concluded that thevoltage level of the sawtooth signal exceeds the first referencevoltage. Depending on whether the voltage level of the sawtooth signalexceeds the second reference voltage or not, the control logic 130 maydecrease or retain the voltage level of the sawtooth signal.

If a negative determination is made at 406, the method 400 proceeds todetermining whether the second comparison signal is asserted at 410. Ifa positive determination is made at 410, the control logic, at 412,outputs of the control signal commanding the sawtooth signal generationstage to decrease the voltage level of the sawtooth signal. For example,the control logic 130 may decrease a level of the control signal. If anegative determination is made at 410, the control logic 130, at 414,causes the voltage level of the sawtooth signal to be retained. Thecontrol logic 130 may cause the voltage level of the sawtooth signal tobe retained by retaining the level of the control signal at its presentlevel. The method 400 may be continuously repeated cycle-by-cycle. After408, 412 or 414, the method 400 may revert to 402.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A sawtooth signal generator, comprising: asawtooth signal generation stage including a current source, thesawtooth signal generation stage configured to: receive a controlsignal; and generate a sawtooth signal based on the control signal, thesawtooth signal having a peak voltage and a minimum voltage; a firstcomparator configured to: receive a first reference voltage, the firstreference voltage being greater than the minimum voltage; receive thesawtooth signal; compare the peak voltage of the sawtooth signal withthe first reference voltage; and output a first comparison signal thatis asserted when the peak voltage of the sawtooth signal exceeds thefirst reference voltage and deasserted when the peak voltage of thesawtooth signal does not exceed the first reference voltage; a secondcomparator configured to: receive a second reference voltage, the secondreference voltage being greater than the first reference voltage;receive the sawtooth signal; compare the peak voltage of the sawtoothsignal with the second reference voltage; and output a second comparisonsignal that is asserted when the peak voltage of the sawtooth signalexceeds the second reference voltage and deasserted when the peakvoltage of the sawtooth signal does not exceed the second referencevoltage; control logic configured to: receive the first and secondcomparison signals; determine whether the first comparison signal isdeasserted; in response to determining that the first comparison signalis deasserted, output the control signal to the sawtooth signalgeneration stage to increase a slope of the sawtooth signal using thecurrent source; determine whether the second comparison signal isasserted; and in response to determining that the second comparisonsignal is asserted, output the control signal to the sawtooth signalgeneration stage to decrease the slope of the sawtooth signal using thecurrent source; and the sawtooth signal generation stage furtherconfigured to: in response to the control signal output from the controllogic, increasing or decreasing the current source to output the peakvoltage of the sawtooth signal between the first reference voltage andthe second reference voltage.
 2. The sawtooth signal generator of claim1, wherein the sawtooth signal generation stage includes: the currentsource having a control terminal configured to receive the controlsignal, an anode coupled to a voltage supply node and a cathode coupleda sawtooth signal output node; a capacitance having a first side coupledto the output of the sawtooth signal output node and a second sidecoupled to a reference node; and a switch having a control terminalconfigured to receive a reset signal, a first conduction terminalcoupled to the sawtooth signal output node, and a second conductionterminal coupled to the reference node.
 3. The sawtooth signal generatorof claim 2, wherein the current source is configured to: receive thecontrol signal; and adjust an output current provided at the cathodebased on the control signal.
 4. The sawtooth signal generator of claim2, wherein the control logic is configured to: receive a clock signal;and output the reset signal based on the clock signal, the reset signalwhen activated causes the switch to close and reset the sawtooth signalto a reference voltage of the reference node.
 5. The sawtooth signalgenerator of claim 1, wherein the control logic is configured to:determine that the first comparison signal is asserted and the secondcomparison signal is deasserted; and in response to determining that thefirst comparison signal is asserted and the second comparison signal isdeasserted, output the control signal commanding the sawtooth signalgeneration stage to retain the slope of the sawtooth signal.
 6. Thesawtooth signal generator of claim 1, wherein increasing the slope ofthe sawtooth signal increases the peak voltage of the sawtooth signaland decreasing the slope of the sawtooth signal decreases the peakvoltage of the sawtooth signal.
 7. A controller for a converter,comprising: a switching stage configured to: receive a feedback voltageindicative of an output voltage of the converter, and a sawtooth signal,the sawtooth signal having a peak voltage and a minimum voltage;generate a control signal based on the feedback voltage and the sawtoothsignal; and output the control signal for driving the converter; and asawtooth signal generator configured to: receive a first referencevoltage and a second reference voltage, the first reference voltagebeing greater than the minimum voltage and the second reference voltagebeing greater than the first reference voltage; determine whether thepeak voltage of the sawtooth signal is less than the first referencevoltage or greater than the second reference voltage; in response todetermining the peak voltage is below the first reference voltage,increase a current source to output the peak voltage of the sawtoothsignal between the first reference voltage and the second referencevoltage; and in response to determining the peak voltage is greater thanthe second reference voltage, decrease the current source to output thepeak voltage of the sawtooth signal between the first reference voltageand the second reference voltage.
 8. The controller of claim 7, whereinthe sawtooth signal generator is configured to: receive a clock signalfor operating the converter; and cause a voltage level of the sawtoothsignal to be reset in response to the clock signal.
 9. The controller ofclaim 8, wherein the sawtooth signal generator is configured todetermine whether the voltage level of the sawtooth signal is below thefirst reference voltage or greater than the second reference voltageprior to causing the voltage level of the sawtooth signal to be reset.10. The controller of claim 7, wherein the current source has a controlterminal, an anode coupled to a voltage supply node, and a cathodecoupled to a sawtooth signal output node, wherein the sawtooth signalgenerator further includes: a capacitance having a first side coupled tothe sawtooth signal output node, and a second side coupled to areference node; and a switch having a control terminal for receiving areset signal, a first conduction terminal coupled to the sawtooth signaloutput node, and a second conduction terminal coupled to the referencenode.
 11. The controller of claim 10, wherein the switch is configuredto transition to an electrically conductive state in response toassertion of the reset signal to reset the sawtooth signal to areference voltage level.
 12. A method, comprising: receiving a sawtoothsignal from a sawtooth signal generation stage; maintaining a peakvoltage of the sawtooth signal between a first reference voltage and asecond reference voltage, the sawtooth signal having a minimum voltage,the first reference voltage being greater than the minimum voltage, themaintaining including: comparing, by a first comparator, the sawtoothsignal to the first reference voltage; outputting a first control signalin response to the sawtooth signal being less than the first referencevoltage; comparing, by a second comparator, the sawtooth signal to thesecond reference voltage; outputting a second control signal in responseto the sawtooth signal being greater than the second reference voltage;increasing the peak voltage in response to the first control signal; anddecreasing the peak voltage in response to the second control signal.13. The method of claim 12, comprising: supplying, by a current sourceof the sawtooth signal generation stage, current to charge acapacitance; and drawing the sawtooth signal from a charge on a firstside of the capacitance.
 14. The method of claim 13, comprising:receiving, by the current source, a digital multibit signal; andincreasing or decreasing, by the current source, a supply of current tothe capacitance based on the digital multibit signal.
 15. The method ofclaim 14, wherein the digital multibit signal has a digital valuerepresentative of a level of the current supplied by the current sourceto charge the capacitance.
 16. The method of claim 12, comprising:supplying the sawtooth signal to a controller of a converter.
 17. Themethod of claim 16, comprising: detecting that a clock signal used tooperate the converter transitioned between states; and in response todetecting that the clock signal transitioned between states, resettingthe sawtooth signal to a reference voltage.
 18. The method of claim 17,wherein comparing the sawtooth signal to the first reference voltage andcomparing the sawtooth signal to the second reference voltage isperformed prior to resetting the sawtooth signal.